Specific Effect of Peculiar Velocities on Dark-Energy Constraints from Type Ia Supernovae

TL;DR

Peculiar velocities of SNIa host galaxies introduce a predictable bias in dark-energy parameter estimates, which can be mitigated with small modifications to current analysis methods.

Contribution

This paper demonstrates that peculiar velocities cause a specific, predictable bias in dark-energy constraints from SNIa data and proposes simple modifications to reduce this effect.

Findings

Bias in parameters is in a known direction for given datasets

Simulation and data analysis confirm the bias pattern

Small analysis modifications can effectively eliminate the bias

Abstract

Peculiar velocities of type Ia supernova (SNIa) host galaxies affect the dark-energy parameter constraints in a small but very specific way: the parameters are biased in a single direction in parameter space that is a-priori knowable for a given SNIa dataset. We demonstrate the latter fact with a combination of inference from a cosmological N-body simulation with overwhelming statistics applied to the Pantheon SNIa data set, then confirm it by simple quantitative arguments. We quantify small modifications to the current analyses that would ensure that the effect of cosmological parameters is essentially guaranteed to be negligible.